In hazardous environments, particularly those involving explosive gases or vapors, the electrical switches must be designed to inhibit or prevent ignition of the explosive gases or vapors. Additionally, the switches must be readily accessible for operation within the hazardous environment or exposed to the combustible or explosive gases or vapors.
The switch must have relatively movable parts which must be able move in an easy manner between on and off positions. With these easily movable parts, it is extremely difficult to prevent the entry of the explosive gases or vapors into the switch chamber housing the movable and stationary contacts which make and break the electrical circuit to which they are attached.
During engagement and disengagement of the stationary movable contacts within the contact chamber of the switch, sparks are often generated. The sparks will tend to ignite the explosive or combustible gases which may have seeped into the contact chamber between the relatively movable parts of the switch. The ignition of the gases and vapors within the relatively small contact chamber of the switch can be tolerated. However, the flame or ignited gases and vapors cannot be permitted to escape the switch contact chamber and engage the explosive gases and vapors located exterior to the switch to which the switch is exposed. If the ignited gases or vapors within the contact chamber are permitted to escape, such ignited gases and vapors could ignite the exterior explosive gases or vapors causing a serious explosion.